In the dental field, the oral-maxillo facial field, the orthopedic field or other surgical fields, defects and hollow portions of bones can be formed during highly complicated fractures or removal operations. To fill in these defects, prior art techniques included taking pieces from flank bones or other bones of the patient and filling in the injured portion of bone with these bone fragments. This method is not desirable as the patient suffers pain since bone tissue other than the injured portion is taken out for use. It also requires an extra operation. In addition, a sufficient amount of autoplastic bone cannot always be taken from the patient's body.
Various metals and plastic materials have also been used as substitute materials for bones in the human body. However, metals are difficult to fit to irregular cavities and, even when snugly fitted, cause stress and concomitant trauma to overlying soft tissue or frequently cause the surrounding bone to resorb, thus enlarging the cavity.
Fully polymerized plastics are also difficult to rapidly cut and shape to fit irregular cavities. A commonly accepted approach therefore has been to use a methyl methacrylate/polymethylmethacrylate dough or cement which readily comforms to irregular cavities and polymerizes in place. However, the polymer is relatively brittle and hard and unsuitable for filling cavities which will experience stress. Moreover permanent adhesion to the surrounding bone is rarely achieved.
Both metal and polymeric implant systems have been devised which provide for some measure of void space for ingrowth or attachment to surrounding bone. However, the void space provided is such that ingrowth is limited and a relatively sharp transition remains between the implant and the surrounding bone. This results in stress concentrations which can result in bone resorption and loosening of the implant or trauma to overlying soft tissue.
Biomaterials of ceramics made of single crystalline or polycrystalline alumina (Al.sub.2 O.sub.3), sintered calcium tertiary phosphate (Ca.sub.3 (PO.sub.4).sub.2) and sintered hydroxyapatite (Ca.sub.5 (PO.sub.4).sub.3 OH) have also been used as substitute materials. These materials are not desirable however, as they are hard and brittle.
U.S. Pat. No. 3,443,261 teaches a homogeneous mixture of a water-insoluble, microcrystalline ionizable salt of collagen, calcium phosphate and water. Fibers such as polyesters, nylon, polytetrafluoroethylene (PTFE), polyolefins, and polycarbonates are added to the calcium phosphate mixture to increase the hardness. Calcium phosphates included dicalcium phosphate, tricalcium phosphate, octacalcium phosphate, hydroxyapatite, carbonate apatite, chlorapatite, fluoroapatite and mixtures thereof. The relative hardness, flexibility, plasticity, and rigidity were dependent on the relative proportions of the organic and inorganic constituents and structural morphology.
U.S. Pat. No. 4,373,217 teaches an implantation material comprising a polymeric base of an acrylate, a polymethacrylate and a methacrylate or a mixture thereof, and 5-35% by weight of resorbable tricalcium phosphate of a particle size of 50-300 um and an available pore volume of less than 0.1 ml/g.
U.S. Pat. No. 4,518,430 teaches an implantation composition comprising tetracalcium phosphate and at least one other sparingly soluble calcium phosphate solid in equilibrium with a dilute aqueous solution.
U.S. Pat. No. 4,497,075 teaches the use of powders of a calcium phosphate compound having apatite crystalline structures or apatite calcium phosphate compounds which include hydroxyapatite having the general formula Ca.sub.m (PO.sub.4).sub.n OH (1.33.ltoreq.m/n.ltoreq.1.95). The crystallite size of the apatite calcium phosphate compound is described to be 400 A.degree. or larger, while the crystal grain size of the same compound should be 3 um or smaller.
The implantable materials comprised of calcium phosphates and derivatives thereof as described above have several drawbacks in that none provide for resilience and strength. In addition, they lack a high void volume and/or large enough void channels to provide for potential living tissue ingrowth. Also, tricalcium phosphate or hydroxyapatite powders and granules are deficient in shaping and in maintaining a given shape.